It is known that a radio access network allows a plurality of users provided with respective terminals (e.g. mobile phones, PDAs, laptop PCs, etc.) to access a number of telephone services and/or data services (such as Internet access, text message services and multimedia message services, e-mail, etc.). Exemplary radio access networks are the GSM (Global System for Mobile communications), the UMTS (Universal Mobile Telecommunications System) and the LTE (Long Term Evolution networks).
A radio access network typically comprises a plurality of network nodes (or simply nodes) and a traffic collection center. For instance, in a GSM radio access network the traffic collection center is termed BSC (Base Station Controller). The nodes and the traffic collection center are connected to each other according to a given topology (e.g. tree or ring) by means of point-to-point wireless connections.
Each node collects traffic from terminals located within its own coverage area (termed “cell”) and forwards it to the traffic collection center possibly through other nodes. This type of traffic is generally termed “upstream traffic”. On the other hand, each node receives traffic from the traffic collection center, possibly through other nodes, and distributes it to terminals located in its cell. This type of traffic is generally termed “downstream traffic”. Nodes located at the edge of a radio access network will be termed herein after “terminal nodes”, while all the other nodes of the radio access network will be termed “intermediate nodes”.
Each node (either terminal or intermediate) typically comprises an access device for collecting/distributing traffic in the cell and a microwave apparatus (which is generally termed “backhauling apparatus”) for implementing the above point-to-point connections with the adjacent nodes. For instance, in a GSM radio access network the access devices are typically called BTS (Base Station Transceiver), while in a LTE radio access network the access devices are typically termed eNodeB (Evolved NodeB).
An access device typically comprises one or more transceivers and a digital unit. For instance, in a eNodeB of an LTE radio access network, the transceivers are termed RRH (Remote Radio Head). The access device may have a “split” architecture, i.e. the transceiver(s) may be located outdoor (e.g. they may be fixed to the upper part of a pylon), while the digital unit may be implemented as a separated indoor unit (e.g. located in a cabinet placed at ground level in proximity of the pylon). The transceiver(s) are typically connected to the digital unit by means of respective links, that are typically implemented as optical fiber links or coaxial links. Further, power supply lines are provided for transferring power supply from the digital unit to the transceiver(s).
A backhauling apparatus typically comprises an outdoor unit comprising one or more microwave transceivers (e.g. fixed to the upper part of a pylon) and an indoor unit (e.g. located in a cabinet placed at ground level in proximity of the pylon). The outdoor unit and the indoor unit are typically connected by means of a link, that is typically implemented as an optical fiber link or a coaxial link. Further, a power supply line is provided for transferring power supply from the indoor unit to the outdoor unit.
The access device of a node is connected to the backhauling apparatus. In particular, the digital unit of the access device typically has a backhauling interface connected to the indoor unit of the backhauling apparatus by means of a backhauling link. Also the backhauling link is typically implemented as an optical fiber link or a coaxial link.
In a terminal node, each transceiver of the access device collects traffic in the form of radio signals from terminals located in the cell, formats such radio signals according to the CPRI (Common Public Radio Interface) standard and transmits them to the digital unit. The digital unit performs base-band conversion of the received signals, and multiplexes them so as to form a single upstream traffic flow. The digital unit then transmits the upstream traffic flow to the indoor unit of the backhauling apparatus, by means of the backhauling interface and the backhauling link. For instance, in case of LTE networks, the backhauling link may support Ethernet at the link layer of the Internet Protocol suite, while it may support IP/IPSec (Internet Protocol Security) and the User Plane and Data Plane protocols of LTE (for instance S1 or X2) at the Internet layer of the Internet Protocol suite.
The indoor unit typically splits the upstream traffic flow in upstream packets (typically, Gigabit Ethernet packets) and, according to a routing table, routes each upstream packet to one of the microwave transceivers of the outdoor unit. It shall be noticed that, in LTE networks where the backhauling link supports Ethernet at the link layer, the upstream traffic flow received at the indoor unit through the backhauling interface is already split in Ethernet packets. The operation of splitting the upstream traffic flow in packets has indeed already been performed by the digital unit of the access device before transmission through the backhauling interface and the backhauling link. The microwave transceivers of the outdoor unit therefore receive upstream packets from the indoor unit and transmit them to backhauling apparatuses of further nodes or to the traffic collection center in the form of microwave signals.
On the other hand, at the terminal node the microwave transceivers of the outdoor unit receive downstream packets (typically, Gigabit Ethernet packets) from backhauling apparatuses of further nodes or from the traffic collection center in the form of microwave signals. The microwave transceivers forward the downstream packets to the indoor unit, that processes the packets for recovering a downstream traffic flow and forwards the downstream traffic flow to the digital unit of the access device by means of the backhauling link and the backhauling interface. The digital unit demultiplexes the downstream traffic flow, thus deriving a number of base-band signals, and converts the base-band signals in corresponding signals formatted according to the CPRI standard. The digital unit then forwards such signals to the transmitter(s), and the transmitter(s) distribute them in the form of radio signals to the terminals located in the cell.